Fuel Effeciency in driving.

Randomed by Rituraj / at 5:19 PM / /

I have been doing some driving alone on a straight road with less traffic. The manner in which other vehicles move has had me thinking as to how one can achieve maximum fuel efficiency.
At first I thought more the acceleration more the force and hence more the energy required. But I was wrong since energy required is only the change in kinetic energy. So most of the fuel consumed depends on your final speed. Although this condition applies to ideal cases, it majorly determines the fuel consumed. However, more acceleration DOES require more fuel since more fuel is wasted due to the nature of the engine. I wont go deeper since it does not affect the efficiency as much. Speed or kinetic energy is the dominant determining factor.
What actually can make one achieve maximum efficiency is the speed at which one drives. Driving the car in the highest gear with the optimum RPM is what we keep hearing will consumer lesser fuel. However, although this is theoretically correct, achieving it practically only results in the wastage of more fuel. What usually happens is that the traffic doesn't always move at an optimum speed owing to traffic signals, jams and other numerous inconsistencies. Let me explain:
Let the optimum speed-RPM for my car be the 5th gear at 50kmph. Say I accelerate and reach this speed. But then there is a traffic signal after 100m. So I slow down the car by braking. And what is braking - wasting away all the kinetic energy achieved & consequently wasting fuel too.
After doing some calculations I have arrived at the conclusion that one should drive at lesser speed with optimum RPM such that there is no or minimum usage of brakes. In the case stated above, say the signal turns green after 10 seconds.
50kmph = 13.88 m/s
So I reach the signal in 100/13.88 = 7.2s
Thus I have to decelerate since the signal turns green after 10s.
Instead, I drive at 10m/s which is 36km/h. I reach the signal exactly when it turns green! And the gear that I must drive in order to achieve optimum RPM at 36km/h is the 3rd gear.
Similarly, one also has to slow down due to other vehicles. So the popular and wrong approach is that I accelerate to reach, say 50km/h, and then decelerate to, say 30km/h, which is the speed at which the traffic is moving. The correct approach is
1. Drive at the slowest traffic speed irrespective of the vehicles in immediate vicinity. This will waste some time and draw some angry remarks from fellow drivers. Another approach is
2. Drive at a speed such that you and the (slow)traffic driving ahead of you reach the destination at the same time.
e.g Suppose
Total distance = 100m/s
Your speed = x m/s
Traffic speed = 5m/s
Traffic distance from you = 25m or 75m from destination
Therefore, 100/x = 75/5
or x = 20/3 = 6.66 m/s = 24km/h
The above calculation shows that instead of driving at 50km/h in the 5th gear, you will achieve more eefficiency if you drive at 24km/h in the 3rd gear.
Of course, there are many more variables present to consider but I think eliminating the variables considered above will definitely improve the fuel efficiency.